The invention relates to the field of light-emitting diode (“LED”) lamps, specifically LED lamps capable of being dimmed to reduce energy usage and prolong the life of the lamp.
Lamps of all kinds, whether incandescent, halogen, sodium vapor, or LED, produce heat as a byproduct of the electrical production of light. The hotter the lamp temperature becomes the shorter the life of the lamp. Lamps are typically designed to provide a designed life at a specified voltage and amperage. For instance, a typical incandescent bulb powered with 110 volts of AC power that draws 25 to 110 W has a typical life expectancy of 2,000 hours. If the voltage applied to an incandescent lamp's filament is reduced by 5%, the life of the bulb is doubled and the light output is reduced by approximately 20%. Thus, it is known in the art that dimming a lamp results in prolonged life.
Energy prices have generally risen above the rate of inflation since the 1970's, and energy efficiency has become increasingly important in the global economy. Lamps of all kinds are subject to increasing energy efficiency standards, and the United States has passed laws phasing out inefficient incandescent bulbs by 2014.
LED lamps represent one type of lighting technology vying to replace incandescent bulbs on the market. Typical LED lamps have several LEDs mounted in series to a circuit board. LEDs are semiconductors in which the current flows in only one direction; that is, typical LED lamps require DC current for proper operation. For years, this property led to a limitation on AC-powered LEDs in which an AC-DC converter was required as part of the LED lamp. Such a converter is inherently inefficient, as it serves as an additional source of heat and requires space not available in many lamp applications. Thus, it is an object of the invention to provide a dimmable LED lamp that utilizes AC power without requiring a separate AC-DC converter.
U.S. Pat. No. 7,417,259 (the “'259 patent”) discloses an LED lamp that natively runs on AC power. To achieve this, the '259 patent discloses two sets of LEDs wired in series, with each set having an opposite polarity. Thus, when alternating current is applied to the circuit, one set of LEDs is alternatively lit at any given time. The '259 patent thus provides an LED lamp that runs on AC power without the necessity of an AC-DC converter; however, the LED lamp disclosed in the '259 patent is not capable of being dimmed without flickering due to the inherent instability of AC current. That is, in virtually all applications, it is well known that AC power supplied by the public grid will fluctuate in both voltage and frequency, yet the '259 patent does not account for such fluctuations. It is thus an object of the invention to provide an AC-powered LED lamp that is also capable of being dimmed by various dimming circuit means.
Dimming devices are well known in the art. For example, U.S. Pat. No. 794,983 (the “'983 patent”) discloses a rheostat, which is a device used to vary the resistance in a circuit, thus varying the voltage available to the rest of the circuit. Rheostats are capable of dimming incandescent bulbs by reducing the voltage across the filament of the incandescent bulb. While rheostats are well suited to dimming an incandescent bulb, rheostats are not as efficient as some would believe because rheostats do not actually reduce the power used by the circuit; rather, the power is converted to heat by the rheostat. Thus, the energy is not converted to light by the incandescent bulb filament. It is an object of the invention to provide a dimmable LED lamp in which the actual circuit power consumption is reduced when the LED lamp is dimmed by a user.
Traditional rheostats are standard dimming devices used in the lighting industry, making them commercially viable for retrofit uses of AC-powered LED lamps. However, no prior art solves the problem of flickering when using a rheostat with an AC-powered LED lamp. To illustrate, while incandescent bulb filaments produce both heat and light proportional to the voltage applied across such filaments, LEDs require a minimum “on voltage” to be operable. The on voltage for an LED depends on the current applied and the type of semiconducting material from which the LED is made, but the on voltage is always significant. Due to this limitation, AC voltage waves for LEDs are said to be “square waveforms,” whereas AC voltage waves for incandescent bulbs are more typically sinusoidal waveforms. Thus, instead of having three points in time at which the voltage is zero as in a sine wave, a square wave for an LED has three much longer discrete blocks of time during which the voltage is zero. When a rheostat is connected to an LED lamp, the square wave defined by the on voltage creates an unwanted visible flicker. It is thus an object of the invention to provide an AC-powered LED lamp that does not have such a visible flicker.
Other dimming devices standard in the industry include silicon-controlled rectifiers (“SCRs”) and triodes for alternating current (“TRIACs”). When these types of semiconducting dimmers are used to dim an AC-powered LED lamp, the phase-controlled sinusoidal voltage waveform nonetheless results in a visible flicker and other unwanted harmonics. It is thus an object of the invention to provide an AC-powered LED lamp that does not have a visible flicker, regardless of the dimming circuitry used. It is a further object of the invention to provide an AC LED lamp capable of being connected to a rheostat, SCR dimmer, TRIAC dimmer, or other dimmer known in the prior art, thus achieving the goals of power savings and reduction of heat, even in retrofit applications.